"We saw the fire pulsating, coming out of the hall. Those who managed got out and those who didn't got stuck."
The hacker has been arrested after the x-rated content was seen by passers-by.
Powerful Shi'ite cleric Moqtada al-Sadr said he would quit politics, causing the wild scenes.
The attack did not cause any casualties.
As rescuers combed the smoke-charred building, Prime Minister Mustafa al-Kadhimi blamed negligence .
